Negative-acknowledge character
Encyclopedia
- In telecommunicationTelecommunicationTelecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
s, a negative-acknowledge character (NAK or NACK) is a transmissionTransmission (telecommunications)Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
control characterControl characterIn computing and telecommunication, a control character or non-printing character is a code point in a character set, that does not in itself represent a written symbol.It is in-band signaling in the context of character encoding....
sent by a station as a negative responseAnswerGenerally, an answer is a reply to a question or is a solution, a retaliation, or a response that is relevant to the said question.In law, an answer was originally a solemn assertion in opposition to some one or something, and thus generally any counter-statement or defense, a reply to a question...
to the station with which the connection has been set up. - In Binary Synchronous CommunicationsBinary Synchronous CommunicationsBinary Synchronous Communication is an IBM link protocol, announced in 1967 after the introduction of System/360. It replaced the synchronous-transmit-receive protocol used with second generation computers. The intent was that common link management rules could be used with three different...
protocolCommunications protocolA communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
, the NAK is used to indicate that an errorErrorThe word error entails different meanings and usages relative to how it is conceptually applied. The concrete meaning of the Latin word "error" is "wandering" or "straying". Unlike an illusion, an error or a mistake can sometimes be dispelled through knowledge...
was detected in the previously received blockBlock (telecommunications)In telecommunications a block is one of:* A group of bits or digits that is transmitted as a unit and that may be encoded for error-control purposes....
and that the receiver is ready to accept retransmissionRetransmission (data networks)Retransmission, essentially identical with Automatic repeat request , is the resending of packets which have been either damaged or lost. It is a term that refers to one of the basic mechanisms used by protocols operating over a packet switched computer network to provide reliable communication...
of that block. - In multipoint systems, the NAK is used as the not-ready reply to a poll.
- In the ASCIIASCIIThe American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
code, the NAK character is 0x15 (hexadecimalHexadecimalIn mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
), or ^U.